If the state opens up this contract to gays, it starts the process of decreased expectations on that contract. The fear is that the marriage contract will loose its meaning over time.
imho, you've nicely outlined the only decent non-religious argument against gay marriage.
what i would ask you is what exactly are a couple's obligations to the state under a marriage contract? and would you not say that the contract has already lost its traditional meaning in a society which has adopted a liberal attitude toward contraception, fornication, adultery, and divorce?
There are a number of tangible and intangible obligations but the two main obligations are raising the children and caring for the other spouse. The primary interest of the state in a divorce is that a financially incabable spouse is not abandoned to the state and that the children are cared for.
and would you not say that the contract has already lost its traditional meaning in a society which has adopted a liberal attitude toward contraception, fornication, adultery, and divorce?
I think it has but I don't think society's expectations have decreased all that much regarding marriage. 2000 years ago Jesus was complaining about the morality of his time. Will gay marriage change the social contract for better or worse ? I don't know but I think there is a far better chance of the a new contract surviving if its written by the majority rather than waiting for it to be forced on everyone.